Due to environmental and scenario constraints, direct measures of the metabolic demands of work can be difficult or impossible. Fortunately, cardiorespiratory variables respond in a predictable fashion with work rate, and can serve as surrogate indices for approximating energy expenditure (e.g. heart rate and minute ventilation). However, a failure to fully explore the utility of these indices during field-based work is a major limitation within the literature. Thus, this investigation was aimed at evaluating the transferability of predictive equations developed in the laboratory to a series of fire-fighting simulations conducted in the field.